Under current underground mining engineering practices, mine passageways such as portals, adits, drifts, inclines and shafts are constructed to follow the course of mineral veins and to provide access for men and machinery so that they can penetrate, detach an convey mineral bearing materials to external processing facilities. Such activities do however produce several major safety concerns. First and foremost is the fact that, as raw passageways are opened, there usually must be erected some sort of ceiling to prevent the fall of loose material on to personnel and/or equipment working below. These ceilings are often supported by vertical strength members of sufficient strength to support a ceiling and/or the roof of the raw pasageway itself. Such passageways are then very often given a coating of a mine sealant material. These mine construction procedures generally result in passageways having a tube-like character. Ideally, such tubes should at least have enough structural integrity to aid in resising the fall of loose material from the roof and/or incursions of loose materials from the sides of such passageways. It should be noted at this point that the expressions "roof", "ceiling", and "wall(s)" may be used somewhat loosely and even intechangeably in the context of describing theee tube-like structures to denote their tops, sides etc.
These tube-like passageways also sometimes serve to channel mine water drainage in desired directions. Obviously, they also serve as convenient distribution channels for the electrical, compressed air, and/or hydraulic fluid lines needed for mining operations. In any event, these tube-like structures are usually completed by covering their surfaces with a mine sealant coating and then providing them with utilities for carrying on further construction activities; not the least of which is the provision of an air supply capable of supporting human life.
Concern for the air supply often make it necessary to line the roofs and walls of the tube for the specific purpose of preventing dissipation of the air supply. In other words, in the absence of a mine sealant coating, the air demand might tend to become insatiable as the mine grows more and more extensive and complex and as more and more points of air leakage have the opportunity to develop. Use of such mine sealant coatings in these tubes also serves to keep out mine gases that would otherwise intrude into the mine's atmosphere as these gases are often present, or formed, as mining operations progress. Concern for the quality of a mine's air supply also often dictates that a tube be "compartmentalized" by placement of air tight walls at selected places across openings formed by particular mine tub sections.
These tubes and the partitions used to compartmentalize them are often constructed from cinder blocks, jute brattices, and timbers. These materials are usually selected for their ease of assembly, relative light weight, strength and low cost. Such construction materials (especially timber and jute) are however often flammable. Moreover, the finishes provided by these materials (e.g., jute brattices) are not usually "air tight". It should also be noted that raw cut mine walls usually have untold numbers of interstices and other irregularities which may detract from their structural integrity. Hence, it is usually necessary to provide them with an internal surface material which can fill, seal and smooth the walls and intersections of various mine architecture elements as well as any interstices and irregularities in the mine's walls, roof, etc.
Ideally, such an internal surface sealant material should have sufficient body to: (1) even out wall irregularities and interstices, (2) seal the tube against undue air supply losses and mine gas incursions as well as serve to channel the mine's air supply toward desired areas, (3) at least assist in preserving the structural integrity of the tube system and, ideally, also (4) serve to suppress flame propagation of wall and mine architecture materials in case of fire and (5) provide a high reflectivity of light in order to conserve illumination within a mine for reasons of safety and improved working conditions.
Many of the most wddely used mine wall sealant compositions use cementitious materials or sulfur as their basic ingredients. However, miners have found that the use of either of these two types of mine sealants presents certain problems and drawbacks. For example, cementitious materials must be mixed on site. This requires a water supply, specialized mixing equipment and utilities at the point where the sealant is being mixed and applied. Ideally, mine sealant materials should be sprayable because hand application is expensive, time consuming and tiiing. However, miners have found that if cementitious materials are diluted to a point where they are sprayable, they do not set up quickly and/or the resulting mine sealant coatings lack structural integrity when they do set up. Consequently most cementitious mine sealants are in fact applied at a very thick, unsprayable consistency by use of hand trowels.
Sulfur based mine sealants have overcome some of he drawbacks associated with cementitious sealants because many sulfur based mine sealants can in fact be supplied to the miner in a sprayable form. They also set up with an acceptable degree of structural integrity. Hence several sprayable, plasticized sulfur coating compositions have been employed for coating mine walls in order to both strengthen the overall structural integrity of the tube and/or to reduce the passage of gases and fluids through a mine's walls, roof and architecture. Such compositions are generally composed of sulfur, a liquid polysulfide polymer and glass fibers from about one quarter to one half inch in length. These compositions do have certain drawbacks however. For example, they are sometimes difficult to apply with certain kinds of spray equipment because their glass fiber ingredients tend to clog many spray nozzles commonly employed in spraying operations. Unfortunately, these materials have to be mixed and aged on site. This is perhaps their greatest drawback. They also exhibit a certain tendency to drip and run from mining wall surfaces if they are diluted enough to be more readily sprayed. Consequently, in practice, many sulfur based mine sealants are also applied with a trowel. Moreover, many sulfur based mine sealants are rather expensive and they tend to give off objectionable odors and/or are iirritating to the eyes.
In response to these problems, other sulfur based compositions containing elemental sulfur, dicyclopentadiene, glass fiber and talc have been introduced. These compositions have proven to be more readily applied to mine walls by spraying than the prior art compositions; they also possess better adhesion qualities over prior art sealants. This attribute has improved the structural integrity and gas imperviousness of the tube and/or raw cut mine walls. In addition, these elemental sulfur compositions exhibit better flame-resistant qualities than most of those of the prior art. They also tend to produce less objectionable odors and they are not nearly as irritating to the eyes. Consequently many present day mine wall coating compositions are compounded from a variety of mixtures of elemental sulfur, dicyclopentadiene, glass fiber and talc mixtures. These elemental sulfur compositions are usually applied to mine walls by spraying a molten mixture of these compositions, preferably at elevated temperatures.
Unfortunately, these compositions also have to be "aged" at elevated temperatures (e.g., 240.degree. to 320.degree. F.) e.g., from about 24 hours to about 48 hours, prior to spraying in order to permit a reaction between the elemental sulfur and the dicyclopentadiene. These elemental sulfur compositions have some other drawbacks as well. For example they often have to be applied to the mine walls at elevated temperatures. Obviously, the equipment needed to produce such elevated temperatures, especially in the context of mining operations, is both expensive and potentially hazardous. Hence it would be of considerable advantage to have other mine sealant compositions which do not require either a heating step as a condition for mixing and/or a long aging period after preparation, but before application. If an alternative material to either cement or sulfur based mine sealants also provided increase structural integrity to the tube upon setting up, and were less costly, so much the better.
Mine wall sealants based upon the use of alkaline metal base ingredients have been suggested as alternative mine sealants. This follows chiefly from the fact that alkali metal ingredients have been used to provide flame-retarding qualities to flammable construction materials employed in non-mining applications. Some of the more common alkali metal based flame retardants are taught in various patent disclosures hereinafter discussed. For example, U.S. Pat. No. 4,179,535 teaches a fire retardant coating made from hydrated metal silicate particles and an aqueous alkali metal silicate solution. A typical coating would comprise sodium silicate and silicon dioxide in a ratio of from about 2 to about 3.5, with the remainder of the coating being comprised of water. However, these alkali metal solutions of this type must be quickly applied as a slurry before any significant absorption of water takes place. Such solution have other drawbacks as well. For example, upon heating, the coatings formed by these materials expand to form a foam and hence they tend to loose any structural integrity they may have had as a hard coating or sealant. In other words they would loose their structural integrity at a time when it was needed most--in the event of fire in a mine.
By way of further example, U.S. Pat. No. 4,066,463 teaches a flame-resistant composition comprising: (a) 20 to 50 weight percent of an aqueous alkali metal silicate solution such as sodium silicate, (b) 5-25 weight percent of a clay such as Kaolin, (c) 2-7 weight percent of deflocculated asbestos fibers, and (d) an organic component such as carboxyl methylcellulose.
U.S. Pat. No. 4,168,175 teaches a fire retardant composition comprised of an admixture of ammonium phosphate, sodium tetraborate containing molecularly bound water and finely ground soda-containing silicate glass for imparting fire retarding property to cellulosic materials.
U.S. Pat. No. 4,277,355 teaches a fireproof coating comprising a non-porous filler e.g., silica flour (or calcium carbonate) dispersed in a water carrier along with a thermo-insulating, porous particulate filler such as slag cinder or lava rock. Alkali metal silicates are employed as a binder.
U.S. Pat. No. 4,338,374 teaches a fireproofing coating made from an alkali metal silicate soluion (e.g., sodium silicate) containing a non-ionic surfactant (e.g., urea, hexamethylenetetramine oorax etc.) in combination an alkali metal tri-silicate (sodium trisiliciate powder).
U.S. Pat. No. 4,376,674 teaches use of flame resistant panels prepared by treating the surface of water-laid fiber mats with an aqueous slurry of sodium silicate and calcium carbonate. The mats are then dried in a prescribed manner.
U.S. Pat. No. 4,419,256 teaches a sprayable building insulation composition comprising a blended mixture of cellulose fiber, mineral wool and expanded silicate glass.
U.S. Pat. No. 4,443,258 discloses a fire retardant material comprised of an unexpended form of perlite associated with a permeable mass of silica glass. Upon exposure to combustion temperatures, the perlite expands from its unexpended form to its expanded form. When exposed to heat, the perlite and glass react to form a flame-impenetrable eramic material.
Such flame-retardant compositions have not, however, for various reasons, proved to be useful as mine sealant materials. This lack of utility usually follows from the fact that those sodium silicate based materials which may be effective air and gas sealants usually must be mixed with a water carrier, on site, where water may be unavailable. They also tend to become very thick so quickly that they become unsprayable. Hence when used, they too generally would have to be applied with a trowel. As previously noted, hand trowel work is slow, expensive, tiring and tedious.
On the other hand, attempts to "thin" such sodium silicate compositions have produced sealant materials which are sprayable, but which also have to be mixed on site and which also tend to dry much too slowly for use in most mining operations. In fact many sodium silicate solutions simply refuse to set up in a hard form in the damp, cold atmosphere usually extant in underground mines. Hence, they provide little or no structural integrity to the tube.
One such sprayable, fire-retardant sodium silicate material, used by a predecessor to applicants' assignee company, was formulated by preparing a two part formulation. The first part of that formulation was prepared by taking sodium silicate and vigorously mixing it with hot water so that the sodium silicate went into solution. To this first solution a fine perlite was added with agitation under heat (110.degree. F.) for one and one half hours. The resulting solution was then cooled to 85.degree.-90.degree. F. A second part of that formulation was prepared by mixing activated silica with a wetting agent. This second part of the formulation was then allowed to stand for 12 hours. The first part and the second part of that formulation were then added together under agitation. Finally, chromium trioxide was added to the mixture as a catalyst. The resulting formulation was in fact sprayable; nevertheless, it proved to be unacceptable to the mining industry for a number of other reasons. Not the least of these was the fact that, under the usual damp and cold conditions encountered in many mine, that formulations also required unacceptably long times (48 hours or more) to dry. Under colder conditions (less than about 40.degree. F.) that formulation sometimes completely refused to set up in the hard form needed to aid in augmenting the structural integrity of a mine tube.